Scale and corrosion control in flowing waters

ABSTRACT

Disclosed is a method of conditioning water, particularly flowing or circulating water streams (e.g., as used in cooling water systems), to reduce the corrosive attack and/or scale accumulation on metal surfaces which the water contacts. The method includes introducing into the water a water soluble cationic polymer and a polyphosphate. The cationic polymer is a polyamide containing quaternary ammonium groups or a polyureylene containing quaternary ammonium groups. The polyphosphate is an inorganic polyphosphate or a polyfunctional acid phosphate ester of a polyhydric alcohol (i.e., a phosphorylated polyol). The cationic polymers synergistically increase the effectiveness of the polyphosphate as corrosion and scale inhibitors in certain waters. A typical inorganic polyphosphate is sodium tripolyphosphate. A typical phosphorylated polyol is phosphorylated pentaerythritol.

nit ttes ate] [1 1 1 1 9 9 Eeeher 1 l eht 119, 10741 SCALE ANDCOlRlROslON CONTROL llN Primary Examiner-Samih N. Zaharna FLOWIIN GWATERS [75] Inventor: David C. Zecher, Newark, Dell [73] Assignee:Hercules Incorporated, Wilmington,

Del.

[22] Filed: Feb. 28, 1972 [21] Appl. No; 230,060

Related US. Application Data [63] Continuation-impart of Ser. No.127,756, March 24,

1971, abandoned.

[52] ILLS. Cl. 210/58, 252/180 [51] 111111. C1 (30% 5/04 [58] Field 01Search 210/58; 21/2.7; 252/180 [56] References Cited UNITED STATESPATENTS 3,639,292 2/1972 Gilby 210/58 3,462,365 8/1969 Vogelsang 210/58Assistant ExaminerBenoit Castel Attorney, Agent, or Firm-Michael B.Keehan [57] ABSTRACT Disclosed is a method of conditioning water,particularly flowing or circulating water streams (e.g., as used incooling water systems), to reduce the corrosive attack and/or scaleaccumulation on metal surfaces which the water contacts. The methodincludes introducing into the water a water soluble cationic polymer anda polyphosphate. The cationic polymer is a polyamide containingquaternary ammonium groups or a polyureylene containing quaternaryammonium groups. The polyphosphate is an inorganic polyphosphate or apoly functional acid phosphate ester of a polyhydric alcohol (i.e., aphosphorylated polyol). The cationic polymers synergistically increasethe effectiveness of the polyphosphate as corrosion and scale inhibitorsin certain waters. A typical inorganic polyphosphate is sodiumtripolyphosphate. A typical phosphorylated polyol is phosphorylatedpentaerythritol,

3 tClaims, No Drawings SCALE AND CUMlEKUSllON CtDNTlRUlL llN MOWTNGWATERS This application is a continuation-impart of my copendingapplication, Ser. No. 127,756, filed Mar. 24, 1971, now abandoned.

The present invention relates to a method of conditioning water, andmore particularly for conditioning flowing or circulating water streams(e.g., as used in cooling water systems) to reduce the corrosive attackand/or scale accumulation on metal surfaces which the water contacts.

Cooling waters are used in many industrial processes to remove heat.Most waters used for this purpose contain dissolved solids which tend toform insoluble deposits (i.e., scale) on metal surfaces which theycontact, particularly the metal components of heat exchangers.

Among the most effective and widely used corrosion and scale inhibitorsat present are formulations based on chromium compounds in thehexavalent oxidation state, e.g., the chromates and dichromates ofsodium, potassium and zinc. However, chromium-based inhibitors haveseveral disadvantages, among the most serious of which are toxicity,staining, and incompatibility with reducing agents (e.g., H S and Soften present in the air drawn through cooling towers. Recently therehas been a substantial increase in demand for nonchromate nontoxiccorrosion and scale inhibitors. Among the nonchromate nontoxic corrosionand scale inhibitors, polyphosphates including more specificallyinorganic polyphosphates have been used and more recently polyfunctionalacid phosphate esters of polyols (i.e., phosphorylated polyols);however, both of these nonchromate classes of polyphosphates aregenerally less efficient corrosion and scale inhibitors than thosecontaining chromate, hence there is a substantial need for increasingtheir efficiency.

According to the present invention it has been found that certain watersoluble cationic polymers increase the efficiency of certainpolyphosphates, as hereinafter defined, as corrosion and scaleinhibitors in certain waters. The increase in efficiency has been foundto be synergistic in many waters depending primarily upon theconstituents present in the water.

The term synergistic is used herein in its usual sense to mean that thereduction in corrosion and/or scale deposition under a given set ofcircumstances using the combination of the present invention (i.e.,cationic polymer plus polyphosphate) is substantially greater than thesum of the corrosion and/or scale deposition results obtained using thecationic polymer alone plus that obtairied using the polyphosphatealone.

Unless otherwise stated, as used herein, the term polyphosphates means(1 inorganic polyphosphates (2) phosphorylated polyols, and (3) thecorresponding acids of l and the term inorganic polyphosphates includesthe corresponding acids thereof.

Polyphosphates applicable herein are:

l an inorganic polyphosphate having a molar ratio of alkali metal oxide,alkaline earth metal oxide, zinc oxide and combination thereof to P 0 ofabout 0.4/1 -2/1, and the corresponding acids of said inorganicpolyphosphates having a molar ratio of water in said inorganicpolyphosphates to P 0 of about 0.4/1 2/1 2. a polyfunctional acidphosphate ester of a polyhydric alcohol, said ester having the formulalR-(-0]PO H )x wherein R is the hydrocarbyl group of a polyhydricalcohol (i.e., R is any remaining organic residue of a polyhydricalcohol used as the starting material) and x is a number from 2 to 6,

said esters often being referred to in the art as phosphorylatedpolyols.

Applicable water soluble inorganic polyphosphates include for instanceany of the water soluble glassy and crystalline phosphates, e.g., theso-called molecularly dehydrated phosphates of any of the alkali metals,alkaline earth metals, and zinc, as well as zinc-alkali metal phosphates(e.g., the compound commercially available as CALGON TG which issubstantially sodium hexametaphosphate containing about 8 percent zinc),and mixtures thereof. The claims herein are also intended to includesaid mixtures. Included also are the acids corresponding to thesepolyphosphate salts, e.g., pyrophosphoric acid (P1 1 0 and higherphosphoric acids having a molar ratio of water to P10; of about 0.4/12/1. Examples of particular inorganic polyphosphate compounds applicableinclude the pyrophosphates (e.g. tetrapotassium pyrophosphate andpyrophosphoric acid), the tripolyphosphates (e.g. sodiumtripolyphosphate), the hexametaphosphates (e.g., sodiumhexametaphosphate).

A number of processes are known in the art for preparing thephosphorylated polyols. A preferred process is to react polyphosphoricacid with a polyol. The polyphosphoric acid should have a P 0 (i.e.,phosphorus pentoxide) content of at least about 72 percent, prefer ablyabout 82 percent to 84 percent. A residue of orthophosphoric acid andpolyphosphoric acid remains on completion of the reaction. This residuemay be as hish 3 4 b?! Z. 40% of theme Weight of h phosphorylatedpolyol. It may either be removed or left in admixture with thephosphorylated polyol. Preferably the phosphorylated polyols produced bythis process are prepared employing amounts of a polyphos phoric acidhaving about 0.5-1 molar equivalents of P 0 for each equivalent of thepolyol used. Larger amounts of polyphosphoric acid can be used ifdesired. By equivalent of the polyol is meant the hydroxyl equivalentsof the polyol. For example, one mole of glycerol is three equivalentsthereof, one mole of pentaerythritol is four equivalents thereof, and soforth. The phosphorylated polyols (acid esters) can be partially orcompletely converted to their corresponding alkali metal salts orammonium salts by reacting with appropriate amounts of alkali metalhydroxides or ammonium hydroxide.

Preferred polyhydric alcohols (e.g., polyols) include ethylene glycol,1,3-propane diol, glycerol, trimethanolethane, pentaerythritol, andmannitol.

Water soluble cationic polymers applicable in the present invention are:

l. a polyamide containing quaternary ammonium groups obtained byreacting a polyalkylene polyamine having two primary amine groups and atleast one secondary amine group with a C -C saturated aliphaticdicarboxylic acid, reacting the resulting polyamide either (a) with analkylating agent, or (b) with epichlorohydrin, or (c) with both (a) and(b) either together or separately in any order, and

2. a polyureylene containing quaternary ammonium groups obtained byreacting a polyalkylene polyamine having two primary amine groups and atleast one tertiary amine group with urea, reacting the resultingpolyureylene with either (a) an alkylating agent, or (b) withepichlorohydrin.

The following are typical examples of the polyamides in (1) above:

A. Polyamides containing secondary amine groups alkylated to convert atleast some of the secondary amine groups to quaternary ammonium groupswith C -C alkyl substituents.

B. Polyamides containing secondary amine groups reacted withepichlorohydrin to convert at least some of the secondary amine groupsto quaternary ammonium groups, including cyclic structures. Cyclicstructures are groups in which one epichlorohydrin reacts with asecondary amine group to convert it to an ammonium salt group, afourmembered ring being formed.

C. Polyamides containing secondary amine groups alkylated withformaldehyde and formic acid and reacted with epichlorohydrin to convertat least some of the secondary amine groups to quaternary ammoniumgroups.

Preferred polyamides in (1) above include, e.g., those obtained byreacting adipic acid with diethylenetriamine, subsequently alkylatingwith formaldehyde and formic acid, then reacting with epichlorohydrinand those obtained by reacting adipic acid and diethylenetriamine,subsequently alkylating with epichlorohydrin.

The following are typical examples of the polyureylcnes in (2) above:

A. Polyureylenes containing tertiary amine groups reacted withalkylating agents to convert at least some of the tertiary amine groupsto quaternary ammonium groups.

B. Polyureylenes containing tertiary amine groups reacted withepichlorohydrin to convert at least some of the tertiary amine groups toquaternary ammonium groups.

Preferred polyureylenes in (2) above include, e.g., those obtained byreacting N,N-bis(3-aminopropyl) methylamine with urea, and subsequentlyreacting with dimethylsulfate or epichlorohydrin.

With reference to the water soluble cationic polymers above, the moleratio of polyalkylene polyamine to dicarboxylic acid is about O.8/l1.4/l(preferably polyalkylene polyabout l/l), a nd the mole ratio of amine tor is abo t -5. (nr ra zlubpw.

Typical examples of water soluble cationic polymers applicable hereininclude those of US. Pat. Nos. 2,926,154, 3,215,654, 3,240,664 and3,311,594.

The following examples illustrate specific embodiments of the presentinvention. In the examples and elsewhere herein parts and ratios are byweight, inorganic polyphosphates and water soluble cationic polymers areon a solids basis, and phosphorylated polyols are on a substantiallywater-free basis unless otherwise indicated. The examples are notintended to limit the present invention beyond the scope of the appendedclaims.

The procedure used for Examples l-12 hereinafter was as follows.

Test solutions were prepared by adding the appropriate amount ofinhibitor to be evaluated to 3,000 ml. of a synthetic cooling water(distilled water to which was added ppm. CaCl '2l-l O, 55 ppm. MgSO 65ppm. A1 (SO.,) -18H O, 300 ppm. Na SO ppm. NaCl, and 10 ppm NaF), thenadjusted to pH 6.75 with NaOH. The test solution was added to the basinof a recirculating heat-treanfer corrosion test loop that consistedprimarily of a glass basin, a centrifugal pump, a heat-transfer section,and a water condenser, all of which were joined with plasticizedpolyvinyl chloride tubing. The heat-transfer section was comprised of anouter glass jacket and a mild steel tubular specimen into which astainless steel cartridge heater was inserted. The test solution waspumped from the basin, through the pump, to the heat-transfer sectionwhere it flowed through the annular space between the tubular specimenand the glass jacket, and finally through the center of the condenserand back to the basin. The solution was constantly aerated by means ofan air sparge in the basin. The flow rate was regulated from zero to 3gal./min., and the temperature of the test solution was maintained at55C.ilC. by maintaining a constant heat output from the cartridge heaterwhile providing cooling by passing tap water through the outer portionof the condenser. The flow rate of the tap water was regulated utilizinga thermoregulator in the basin. The tubular specimens were polished,degreased, and weighed prior to exposure, then inserted and exposed tothe recirculating test solution for 20 hours; in each case, 15.7 in. ofmetal surface area was exposed. After exposure, the tubes were removed,dried, weighed, then immersed in 5 percent sulfuric acid (containing anamine-based corrosion inhibitor) for 3 minutes. at 70C. to remove allscale and corrosion products, dried and reweighed. The differencebetween the original and final weights is referred to herein as theweight loss and is a measurement of the amount of corrosion that thetubular specimen underwent. The difference between the weight of thetubular specimen after exposure, before and after treatment withinhibited acid, is referred to herein as scale deposition, and is ameasurement of the amount of scale and corrosion products deposited ontothe specimen.

In the Tables following Examples l-l4 the values in parenthesis underweight loss due to corrosion and weight gain due to scale deposition arethe deposition data and the values not in parenthesis are the corrosiondata. Likewise, in Examples 121 the apparatus and test proceduresemployed are well known and widely used in this art.

In the examples, the use of the water soluble cationic polymersdescribed herein as the sole additive, gave substantially the samecorrosion results as determined in a like system without any additives.These cationic polymers were found to reduce the scale deposition belowthe level of the deposition when no additive was employed; however, incomparison with the reduction in scale deposition achieved with thepolyphosphates, this scale reduction is not considered of substantialsignificance when the polymers are used alone.

EXAMPLES l-7 Examples l-7 compare the corrosion and scale depositiondata of tubes exposed to test solutions containing variousphosphorylated polyols with and without Polymer A (a polyamidecontaining quaternary ammonium 3,793,194 r or 6,

groups). Further details appear in Table I below.

TABLE 1 ppm. Additive Weight Loss Due to Corrosion and Weight Gain Dueto Scale Deposition. Mg.

Example No. lPhos. Polyol Polymer A (a) Pentaerythritol Glycerol (b)1,3-Propanediol lnositol (b) Mannitol (b) l 60 none 85(162) 152(250)75(l48) l09t I78) 2 6O 73(l06) 5l(92) 63(101) l00(l39l 3 100 none46(138) 52( I58) 36( 'Z9l 4 I00 26(64) 49 134 (68) 5 150 none 36(121)20(66) 49(l03) 6 I50 20 20(39) 20(30) (86) Example 7 was a control runwith 20 ppm. polymer without any phosphorylated polyol, and the resultswere L252 (L3H) (a) Polymer A is a water solu le polyamide containingquaternary ammonium groups obtained by reacting adipic acid withdicthylenetriamine in 1H molar ratio. subsequently alkylating withformaldehyde and formic acid. then reacting with epichlorohydrin toconvert a majority of the secondary amine groups to quaternary ammoniumgroups.

'(b) Each of the water soluble phosphorylated polyols was prepared byreacting LO hydroxyl equivalent of the appropriate polyol with u 1.0molar equivalent of poly-phosphoric acid, expressed as P 0 at 70-l IOC.for 2-4 hours.

EXAMPLES 8 and 9 EXAMPLES l5 and 16 Examples 8 and 9 compare thecorrosion and scale 20 T e P cdurc Used for Examples 15 and 16 hereindeposition data of tubes exposed to test solutions conafter was asfollows. The recirculating heat-transfer taining one of variousinorganic polyphosphates or corrosion test loop employed for this testseries was polyphosphoric acid with and without Polymer A (asubstantially the same as that described for Examples polyarnidecontaining quaternary ammonium groups). l-l4, except provision was madefor periodic addition Further details appear in Table ll below. of freshtest solution to the basin (malrc-up), with si- TABLE ll Weight Loss Dueto Corrosion and Weight Gain Due to Scale Deposition, Mg. (a)

Example No. Polymer A (b) T??? (c) STP (0) HMP (c) Calgon TG" (c) PPA(c) ppm.

8 none 18(33) 23(45) 137(186) 31(78) 28(44) 9 l0 l6(33) l4(26) 54(128)27(58) 18(26) (a) Concentrations of all inorganic polyphosphates andpolyphosphoric acid were 60 ppm., calculated as P0 (b) See definition(a) following Table l. (c) TPPP is tetrapotassium pyrophosphate;

ST? is sodium tripolyphosphate;

l-lMP is sodium hexametaphosphate (Calgon glass);

Calgon T6 is a tradename for a glassy zinc-sodium hexametaphosphate;

PPA is polyphosphoric acid (82-86% P 0 EXAMPLES 10'14 multaneousdischarge (blowdown) of recirculating so- Examples 10-14 compare thecorrosion and scale delution. An initial high-level dosage treatment(3.3 times position data of tubes exposed to test solutions containthatof the maintenance dosage) was employed for 24 ing a particularphosphorylated polyol, i.e., phosphoryhours followed by treatment at themaintenance level lated pentaerythritol (PPE) with and without variousfor the duration of the 14-day period. The corrosion water solublecationic polymers of this invention. Furrates in mils per year (mpy.)and scale deposition in ther details appear in Table III below.milligrams per sguarecentirnctcr ng./cm." of ex- TABLE ill ppm. AdditiveWeight Loss Due to Corrosion and Weight Gain Due to Scale Deposition,Mg.

Example No. PPE Polymer Polymer A (a) Polymer B (b) Polymer C (c) 10none 85(162) 85(162) I 1 60 10 73(106) 73 I2 none 36(121) 36(l2l)36(121) I3 150 20 20 39 151 42 25(64) [4 none 20 l,252(l,313) i,1701,230 1,310 1,400

(a) See definition (a) following Table l.

(h) Polymer B is a water soluble polyamide containing quaternaryammonium groups obtained by reacting adipic acid with diethylenetriaminein H1 molar ratio, then reacting with epichlorohydrin to convert amajority of the secondary amine groups to quaternary ammonium groups.

(c) Polymer C is a water soluble polyureylene containing quaternaryammonium groups obtained by reacting urea with N,N-his(aminopropyl)methylamine in 1/] molar ratio, then reacting withepichlorohydrin to convert a majority of the tertiary amine groups toquaternary ammonium groups.

posed surface area of the tubular mild steel specimens the tradenameCORRATOR from Magna Corporaare given below for test solutions containingeither tion of Santa Fe Springs, California. This corrosion ratephosphorylated pentaerythritol (PPE), inorganic polymeter and its use inthe art is known, and also discussed phosphate or polyphosphoric acidwith and without by C. C. Wright in Journal Petroleum Technology,Polymer A (a polyamide containing quaternary ammopage 269, Mar. 1965,Applying Instantaneous Corronium groups). The maintenance concentrationof addision Rate Measurements t0 Waterflood Corrosion Contive other thanPolymer A was 30 ppm., calculated as trol. Further details appear inTable VI below.

P 41. urt er e s l .a212 n Tablelybslwns i- TABLE IV Corrosion Rate,Mpy. (Scale Deposition. MgJCm) (:1)

Example No. Polymer A (b) ppm. PPE (c) STP (c) Calgon TG" (c) PPA c)none 2.3(50) 3.8(7.8) 3.7 s.4) 0.3 24 l6 6 l.3(l.0) O.4(l.2) O.6(O.7)0.5(05) (a) Values not in parenthesis are corrosion rates, expressed asmils per year, values in parenthesis represent scale deposition inmg./cm. (b) See definition (a) following Table l. (c) PPE isphosphorylated pentaerythritol;

STP is sodium tripolyphosphate;

Calgon TC" is a tradename for a glassy zinc-sodium hexametaphosphate;

PPA is polyphosphoric acid (82-86% P 0 EXAMPLES 17-19 TABLE VI Theprocedure used for Examples l7-l9 below was substantially the same asthat described for Examples Rm, PY- l5 and 16 except using a higher rateof water circula-- Ex- Additive Copper Admiralty Aluminum tion.Pl'OVlSlOll was made for make-up and blowdown No. of the test solution,an initial dosage 3 times that of the d l d f th f. t 24 20 none 1.0 L60.7 maintenance Osage was emp Dye or e "'5 I 2 150 ppm pp 07 Q8 05hours, and the duration of the test was 14 days. In this 20 ppm. Polymermanner, the effects of adding Polymer A to test solu- Nb) t onscontaining 50 ppm. phosphorylated pentaerythimmperywn l'ltOi wasdCtCImlned, Further detalls appear 1]] Table V (b) PPE isphosphorylatedpentacrythritol; PolymcrA isa water soluble polyamide b 1 containingquaternary ammonium groups obtained by reacting adipic acid with e OW'diethylene-triamine in H1 molar ratio, subsequently alkylating withformaldehyde and formic acid, then reactin with e ichloroh drin toconvert a maorit of the TABLEV d w t secon ary amine groups qua ernaryammonium groups.

Example pp (a) polymer corrosipp Rate, Mpyawcale The following examplesillustrate the effect of water p A Deposition, ecomposition on theeffectiveness of the water condipp 40 tioning process of this inventionto reduce corrosive ati; 28 nclme 2.3: tack and/or scale accumulation onmetal surfaces l 9 50 6.7 5 which the water contacts.

(a) PPE is phosphorylated pcntaerythritol.

(b) Sec definition (a) following Table l. o (c) Values not inparenthesis are corrosion rates, expressed as mils per year, values Anaerated synthetlc Cooling water at rein parenthesis represent scale epot n n g-/ circulated at a flow rate of 2.5 ft./sec. through a singletube(mild steel) heat-exchanger in which the mild EXAMPLES 20 and 21 steelheat transfer tube in the exchanger was the specimen under study. Inthese examples a relatively high The Procedure used for Examples 20 and21 herem' inhibitor dosage of 150 ppm. of phosphorylated pentaafter wasas follows. Test solutions (1,509 ml.) were erythritol (polyphosphate)was employed to insure d- P p accordmg to h Procedure describe? forequate initial film formation. The water being recircuamples Thesplutlons were adqed to i kettles lated during these tests is a lowhardness water to which pp with f g p and eqwpped wlth a was addedvarious constituents in designated amounts l g g t0 gnalntam thetemperature 9 h such as interference ions, i.e., aluminum, or potentialf" at 55 9- a Sparge tube to mamtam foulants such as suspended solids.The corrosion and of the Solution and a cndnser to Prevent evap' scaledeposition results after 20 hours of operation of oration losses fromthe test solution. A dual electrode the System are Set forth in TableVII below probe designed to measure instantaneous corrosion r r rateswas immersed in the test solution for 20 hours, TABLE VI] and corrosionrates were measured at that time. Probes containing electrodes of thevarious metals given in wfiight Loss Due to Corrosion and Table VI belowwere used. In this manner, it was found eight Gaindue to Scale that thecombined use of a polyphosphate with a water soluble cationic polymer(Polymer A) was also an ef- Ex. Water Composition" 200 ppm 200 ppmPPE,6O ppm fective corrosion inhibitor for nonferrous metals usu- PPE(b) Polymer A 0:) ally encountered in cooling water systems. The dual 2221W W24) electrode probe used is commercially available under 23 7 lfpprn il g 6 8(94) 43761) TABLE VII-Continued Weight Loss Due toCorrosion and Weight Gain due to Scale Deposition, Mg.

Ex. Water Composition 200 ppm 200 ppm PIPE, 60 ppm No. PPE (b) Polymer A(c) 24 55-1 l ppm A1 0 115(133) 78(92) 25 SS-1+ ppm Fe 19(43) 18(25) 2658-1 50 ppm SiO 125(104) 44(40) 27 55-! 150 ppm 8.5. 34(37) 18(30) 2885-! 30 ppm P04 68(64)d 32(50)d 29 SSl 600 ppm CaCO 58(60)d 43(40)d 333ppm 333 ppm PPE (b), 60 PPE (b) ppm Polymer A (c) 30 55-1 0 ppm A1 0;21(55) (26) 31 88-1 5 ppm Fe 75(128) 48(43) 32 55-1 50 ppm SiO, 32(47)20(21) (d) These results are based on exposure for 3 days rather than 20hours.

In Example 22, the addition of cationic polymer to the phosphorylatedpolyol corrosion inhibitor in accordance with this invention resulted inmarginal improved performance in reducing corrosion. Substantialimprovement in reduction of corrosion and scale deposition isillustrated by Examples 23-32. While not being limited thereto themethod of this invention is most effective for use in water systemscontaining interference ions such as aluminum, and waters containing apotential foulant or precipitant such as silica, iron, suspended solidsor high orthophosphate. Thus, the method of this invention applies towaters in which the combined effect of using the polyphosphates andwater soluble cationic polymers results in reduction of corrosion andscale deposition on metals in contact with the water to a level belowthat achieved when these respective components are employed alone in thewater in like quantities. Characterization of all waters in which suchimprovement will be realized is impossible because of the diverseconstituents in water depending on its source and the condition of thewater when treated. However, one skilled in the art can readilydetermine if the combination of polyphosphate and cationic polymersdefined herein are effective in improving the reduction in corrosion andaccumulation of deposits on metals following the procedures describedherein.

In the method of this invention the amount of inorganic polyphosphateemployed is not critical and may vary widely, depending primarily on theseverity of the corrosion and scale deposition problems. Maintenancedosages of about 5-500 ppm. (often about 20-100 ppm.) by weight areused, calculated as P0,.

The amount of phosphorylated polyol is not critical and may vary widelydepending primarily on the severity of the corrosion and scaledeposition problems. Maintenance dosages of about 5-500 ppm. (oftenabout 20-100 ppm.) by weight are used, calculated as P0 l V l The amountof cationic polymer is not critical and may vary widely dependingprimarily on the amount of inorganic polyphosphate of phosphorylatedpolyol v LII used. The weight ratio range of inorganic polyphos phate(calculated as P0,) to cationic polymer (polymer on solids basis) ofabout 2/1-50/1 (often about 5/- l-l0/ l) is used. The weight ratio rangeof phosphorylated polyol (calculated as P0,) to cationic polyrner(polymer on solids basis of about 2/ 1-50/ 1 (often about 5/ l-10/ l) isused. Expressed as parts per million cationic polymer on solids basis byweight of the water being treated, the amount of cationic polymer isabout 0.2-20 ppm. (often about 2-10 ppm.)

The phosphorylated polyols are usually extremely viscous liquids at roomtemperature. These materials may be diluted and partially or completelyneutralized with an allrali metal or ammonium base to provide a lessviscous solution (e.g., 25%-50%) for easier handling.

The polyphosphates described herein may be added directly to the coolingwater system either periodically or (preferably) continuously, based onthe make-up requirements of the system. It is usually more desirable tofirst dissolve or dilute the polyphosphates with water in a chemicalfeed tank, then pump continuously into the recirculating water. Dilutionto l%l0% at this stage is typical.

The polymers are usually available as viscous aqueous solutions ordispersions. These may be incorporated into formulations containing thepolyphosphates, or may be added to the cooling water separately from thepolyphosphates on a periodic or continuous basis. It is usually moredesirable to first dilute the polymers with water, then pumpcontinuously into the recirculating water separately from thepolyphosphate addition. Thus, the particular manner and form are notcritical in which the phosphorylated polyols, inorganic polyphosphatesand polymers are used.

This invention is applicable to all metals, e.g., ferrous andnonferrous, subject to corrosion and/or scale deposition in circulatingwater systems. These metals include, e.g., mild steel, cast iron, zinc,copper, copperbased alloys, and aluminum.

The method of this invention for the reduction of corrosion and scaledeposition on metal surfaces offers several advantages over the priorart practice of using the polyphosphates alone. in many cooling watersystems where either an inorganic polyphosphate or a phosphorylatcdpolyol has been employed as a corrosion inhibitor, the additional use ofthe polymers described herein will lower the corrosion rates (therebyincreasing equipment life) and substantially reduce further scaledeposition (thereby providing greater heat exchanger efficiencies andpreventing losses in heat transfer ability). In such systems, thecombined use of both components (i.e., polyphosphate and polymer) 5enables the dosage required to maintain a given corrosion rate and scaledeposition rate to be lower for the polyphosphate than is possible inthe absence of the polymer. This has obvious advantages since thepolyphosphate can serve as a nutrient for algae and as a source ofphosphate sludge.

As many apparent and widely different embodiments of this invention maybe made without department from the spirit and scope thereof, it is tobe understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What I claim and desire to protect by Letters Patent 1. Method ofconditioning circulating water to reduce the corrosive attack and scaleaccumulation on metal surfaces which the water contacts which comprisesintroducing into said water a water soluble polyphosphate and a watersoluble cationic polymer, said polyphosphate being a polyfunctional acidphosphate ester of a polyhydric alcohol, said ester having the formulaROPO H )x wherein R is the hydrocarbyl group of a polyhydric alcohol andx is a number from 2 to 6, and said cationic polymer being a polyamidecontaining quaternary ammonium groups obtained by reacting apolyalkylene polyamine having two primary amine groups and at least onesecondary amine group with a C -C saturated aliphatic dicarboxylic acid,reacting the resulting polyamide either (a) with an alkylating agent, or(b) with epichlorohydrin, or (c) withv both (a) and (b) together orseparately in any order, said cationic polymer being employed in anamount of from about 02-20 p.p.m. based on the weight of water beingconditioned and the weight ratio range of polyphosphate to cationicpolymer being from about 2/ l to 50/1, whereby the corrosive attack andscale deposi tion on the metal surfaces is reduced to a level below thatachieved when these respective components are employed alone in thewater in like quantities.

2. The method of claim 1 wherein the amount of cationic polymer employedis from about 2-10 p.p.m. based on the weight of water beingconditioned.

3. The method of claim 2 wherein the range of said polyphosphate to saidcationic polymer is from about 5/1-10/1.

2. The method of claim 1 wherein the amount of cationic polymer employedis from about 2-10 p.p.m. based on the weight of water beingconditioned.
 3. The method of claim 2 wherein the range of saidpolyphosphate to said cationic polymer is from about 5/1-10/1.